Through the opinions of doctors, peasants and workers, this documentary tries to detect what are the causes of parasitosis that significantly affects the majority of the Costa Rica's population.
The story told by the film is simple: a girl is commissioned to investigate parasitosis. At first, she downplays the issue, since she does not believe that, in Costa Rica, this is a serious problem. What she sees seems so serious to her. But as she investigates, inquires, and questions, she notes that in populations without water, in barefoot children, in congested rooms, in the pollution of rivers, in the bulging stomachs of the undernourished, lies the problem of parasitosis. In short, she discovers that the enemy is doubly hidden: in the intestines and entrails of the affected people and in the condition of economic and social underdevelopment of the country.
In the cinematographic aspect, the film has a novel vein within the documentary genre of the film, an actress (the researcher) is introduced who "helps" the viewer to discover where the enemy is hiding.